Communication system, communication unit, control unit, and controlling method

ABSTRACT

Whether or not a signal which is transmitted from a current operation side node to a stand-by side node has been disconnected is determined on a communication route for the signal. When the signal is determined to have been disconnected, the network route is switched to the network route used when a client unit and the stand-by side node perform data communication. With this, the switching of the network route when processing having been performed by a node of a system is performed by another node in place of the node can be made quickly.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of International Application No.PCT/JP2010/051835, filed on Feb. 9, 2010.

TECHNICAL FIELD

The present invention is related to a communication system which astand-by side node performs processing in place of a current operationside node when the current operation side node cannot perform theprocessing, in the communication system including the current operationside node used usually and the stand-by side node different from thecurrent operation side node.

RELATED ARTS

A fail-over is widely used in a communication system which needs aredundancy.

In the fail-over, a stand-by side node is provided separately from acurrent operation side node used usually, and the stand-by side nodetakes over processing when a fault has occurred in the current operationside node.

However, in addition to the taking-over of the processing, it isnecessary that the route setting in the network is switched and thecommunication for the current operation side node must be switched tothe stand-by side node.

Also, when the current operation side node operates again, thecommunication having switched to the stand-by side node must be switchedto the current operation side node again.

A procedure of the switching of the processing from the currentoperation side node to the stand-by side node and the switching of thecommunication route on the network in accompaniment with the switchingof the processing can be described as follows:

(1) The stand-by side node detects a fault in the current operation sidenode;

(2) The stand-by side node shifts to an execution state;

(3) The stand-by side node requests a network route switch to networkunits or a network control unit;

(4) Each of the network units or the network control unit changes thenetwork route (communication route).

However, the network unit means a communication unit such as a routerand a switch, and a network control unit means a unit which controls thenetwork unit.

The above items (1) to (4) are explained in the related art, forexample, JP 2006-253900A (Patent Literature 1).

In Patent Literature 1, (1) when a server in a stand-by mode detects thedisconnection of a heartbeat communication, the operation mode ischanged to the execution mode (2). The server in the stand-by modetransmits a message (for switching the network route) so as to switch aserver in an execution mode to the stand-by mode in a broadcast form(3). The server in the execution mode shifts to the stand-by mode whenreceiving the message (4).

Also, a technique to reduce a time necessary for current operation sidefault detection in the above (1) is disclosed in JP 2002-259155A (PatentLiterature 2).

In Patent Literature 2, a software failure of an application ismonitored and when a fault has occurred, the fault occurrence isnotified to another system at once through an exclusive-usecommunication section. Thus, the fault detection is performed withoutwaiting for disconnection of a heartbeat signal and the fault detectiontime is tried to be shortened.

CITATION LIST

-   [Patent Literature 1]: JP 2006-253900A-   [Patent Literature 2]: JP 2002-259155A

SUMMARY OF THE INVENTION

However, in Patent Literature 1, because the route switching isperformed after the fault detection, it takes time by completion of theroute switching.

Also, in Patent Literature 2, the technique to attempt to reduce a faultdetection time is disclosed, but the route switching on the network isnot considered. Also, in Patent Literature 2, because a time to taken todetect abeyance of the application by a monitoring unit is notconsidered, it is not always possible to reduce the fault detectiontime.

The present invention is accomplished in view of the above situations,and the subject matter of the present invention is to provide acommunication system, a communication unit, a control unit, and acontrol method, in which the switching operation to a network routerequired when an node performs processing having been performed byanother node in a system can be earlier carried out.

The communication system according to the present invention is providedwith a client unit, first and second nodes, communication units and adetermining section. The first node performs processing in response to arequest from the client unit. The second node performs the processing inplace of the first node when a fault has occurred in the first node. Thecommunication units configure network routes between the client unit,the first node and the second node. The determining section is providedonto a first network route and determines disconnection of a signalwhich is transmitted from the first node to the second node through thefirst network route. The communication unit is provided with a switchingsection configured to switch the network route which is used to transferdata from the client unit to a predetermined network address, to anothernetwork route based on the determination result of the determiningsection. The switching section switches the network route between asecond network route used when the client unit and the first nodeperform data communication, and a third network route used when theclient unit and the second node perform data communication based on thedetermination result.

A control method of the present invention is a control method in acommunication system which is provided with a client unit, a first nodewhich performs processing in response to a request from the client unit,a second node which performs the processing in place of the first nodewhen a fault has occurred in the first node, communication units whichconfigure network routes among the client unit, the first node and thesecond node, and a control unit provided onto the first network route.The control method of the present invention includes a step ofdetermining, by a determining section provided onto a first networkroute, disconnection of a signal that which is transmitted from thefirst node to the second node through a first network route; a step ofswitching a network route which is used to transfer data from the clientunit to predetermined network address to another network route based onthe determination result of the determining section. The switching stepincludes switching the network route between a second network route usedwhen the client unit and the first node perform data communication, anda third network route used when the client unit and the second nodeperform data communication, based on the determination result.

It is desirable that the control method of the present invention isrealized by use of a control program which the communication unitsexecute.

Also, the control program of the present invention is a control programto make the control units perform a control method performed in acommunication system which is provided with a client unit, a first nodewhich performs processing in response to a request from the client unit,a second node which performs the processing in place of the first nodewhen a fault has occurred in the first node, communication units whichconfigure network routes among the client unit, the first node and thesecond node, and a control unit provided onto the first network route.In this case, the control method of the present invention includes astep of determining, by a determining section provided onto a firstnetwork route, disconnection of a signal that which is transmitted fromthe first node to the second node through a first network route; a stepof switching a network route which is used to transfer data from theclient unit to predetermined network address to another network routebased on the determination result of the determining section. Thecommunication units switch the network route between a second networkroute used when the client unit and the first node perform datacommunication, and a third network route used when the client unit andthe second node perform data communication, in response to a controlsignal.

According to the present invention, the switching operation of thenetwork route which is required when a node performs processing whichhas been performed by another node of a system can be quickly performed.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, effects, and features of the present invention could beunderstood in conjunction with the description of the exemplaryembodiments and the following drawings:

FIG. 1 is a diagram showing a system configuration of a communicationsystem according to a first exemplary embodiment of the presentinvention;

FIG. 2 is a diagram showing a configuration of a communication unit;

FIG. 3 is a diagram showing a table configuration of a flow table;

FIG. 4 is a diagram showing a communication route in a state before afault occurs in a current operation side server;

FIG. 5 is a diagram showing a communication route in a state after thefault has occurred in the current operation side server;

FIG. 6 is a diagram showing a system configuration of the communicationsystem according to a second exemplary embodiment of the presentinvention;

FIG. 7 is a diagram showing a configuration example of a control unit;

FIG. 8 is a diagram showing a configuration of a communication unit;

FIG. 9 is a diagram showing a communication route in a state before afault occurs in the current operation side server;

FIG. 10 is a diagram showing a communication route in a state after thefault has occurred in the current operation side server;

FIG. 11 is a diagram showing a table configuration of a flow table;

FIG. 12 is a diagram showing a communication route when the currentoperation side server is in a stop state; and

FIG. 13 is a diagram showing a communication route when the currentoperation side server is in an operation state.

DESCRIPTION OF EXEMPLARY EMBODIMENTS First Exemplary Embodiment <SystemConfiguration of Communication System>

Hereinafter, a configuration of a communication system according to afirst exemplary embodiment of the present invention will be describedwith reference to FIG. 1.

The communication system of the present exemplary embodiment is providedwith a client unit 9, a current operation side server 3, a stand-by sideserver 4 and a plurality of communication units 10 to 14.

The current operation side server 3 and the stand-by side server 4 arenodes on which service applications can operate.

The client unit 9 is a unit to utilize the service application whichoperates on the current operation side server 3 and the stand-by sideserver 4.

In the present exemplary embodiment, the current operation side server 3in a normal operation state performs processing of a service requestfrom the client unit 9. When a fault has occurred in the currentoperation side server 3 so that the operation of the service applicationby the current operation side server 3 becomes impossible, the stand-byside server 4 takes over the processing of the current operation sideserver 3 and performs processing of a service request from the clientunit 9.

The determination of whether or not the fault has occurred in thecurrent operation side server 3 is performed by using a heartbeatsignal. In detail, the current operation side server 3 transmits theheartbeat signal to the stand-by side server 4. When receiving theheartbeat signal, the stand-by side server 4 determines that the currentoperation side server 3 is in a normal operation state. When theheartbeat signal cannot be received, the stand-by side server 4determines that the fault has occurred in the current operation sideserver 3.

The communication units 10 to 14 are communication units (network units)such as routers and switches, and network routes 73, 74, and 70 areconfigured between the client unit 9, the current operation side server3, and the stand-by side server 4.

As shown in FIG. 2, each of the communication units 10 to 14 is providedwith a flow table 111, a communication control section 112, and aplurality of communication ports (L to N) 119.

As shown in FIG. 3, the flow table 111 manages a set of “flowinformation”, “output port information”, and “operation information atdisconnection”. With this, the communication units 10 to 14 can controla data transfer destination based on the flow information. Theinformation to be managed in the flow table 111 can be set or changedmanually from an external unit or dynamically by the communication units10 to 14.

The “flow information” is information to specify identificationinformation of each flow. The “output port information” is informationto specify the communication port from which data should be outputted.The “operation information at disconnection” is information showing theoperation to be done when a flow has been disconnected.

For example, according to the flow table 111 shown in FIG. 3, thecommunication units 10 to 14 operate as follows. That is, when receivingdata of a flow A, the communication unit outputs the data of the flow Afrom the communication port N and performs no operation at time ofdisconnection (in the state that the flow A has been disconnected).Also, when receiving data of a flow B, the communication unit outputsthe data of the flow B from the communication port L. On the other hand,when receiving the flow of a network address Z in the state that theflow B has been disconnected, the communication unit outputs the flow ofthe network address Z from the communication port L.

The communication control section 112 refers to the flow table 111 toperform data transfer processing according to the flow table 111. Thecommunication control section 112 is provided with a determining section1121 and a switching section 1122.

The determining section 1121 determines whether or not a network routeshould be switched, based on the heartbeat signal which is transmittedfrom the current operation side server 3 to the stand-by side server 4.The switching section 1122 switches the network route in accordance withthe determination result by the determining section 1121.

<Processing Operation of Communication System>

Next, referring to FIG. 1, FIG. 4, and FIG. 5, the processing operationof the communication system in the present exemplary embodiment will bedescribed. FIG. 4 shows a communication route in a state before a faultoccurs in the current operation side server 3, and FIG. 5 shows thecommunication route in a state after the fault has occurred in thecurrent operation side server 3.

(Precondition)

It is supposed that the current operation side server 3 is operatingnormally, and is in the state that a service request from the clientunit 9 can be processed, as the precondition of the communication systemin the present exemplary embodiment.

The stand-by side server 4 receives the heartbeat signal periodicallyfrom the current operation side server 3. When the heartbeat signal canbe received, the current operation side server 3 is determined to be ina possible state of service provision (an operation state). The stand-byside server 4 shifts to a stand-by mode when the current operation sideserver 3 is in the possible state of service provision. Also, when theheartbeat signal cannot be received in a predetermined period, thestand-by side server 4 determines that the current operation side server3 is in an impossible state of service provision (a fault occurrencestate). The stand-by side server 4 shifts to an execution mode when thecurrent operation side server 3 is in the impossible state of serviceprovision. The stand-by side server 4 uses network addresses used by thecurrent operation side server 3 and takes over the processing beingperformed by the current operation side server 3.

Referring to FIG. 1, the communication route between the client unit 9and the current operation side server 3 is a route 73 through thecommunication unit 10, the communication unit 11 and the communicationunit 13. The route 73 is defined as using the communication port M. Thecommunication route between the client unit 9 and the stand-by sideserver 4 is a route 74 through the communication unit 10, thecommunication unit 11, the communication unit 12, and the communicationunit 14. The route 74 is defined as using the communication port L. Thecommunication route of the heartbeat signal from the current operationside server 3 to the stand-by side server 4 is a route 70 through thecommunication unit 13, the communication unit 11, the communication unit12, and the communication unit 14. The route 70 is defined as using thecommunication port L. Also, the flow of the heartbeat signal is definedas using a flow B.

It is supposed that the current operation side server 3 and the stand-byside server 4 have mechanisms by which mutual communication is madepossible, to transmit and receive the heartbeat signal. For example, itis supposed that the current operation side server 3 and the stand-byside server 4 have the mechanisms which can use a method of assigningdifferent addresses from the addresses used for service provision, amethod of using a name solution system and so on.

It is supposed that the network address used to provide a service to theclient unit 9 is defined as Z and that the current operation side server3 is using the network address Z.

(State Before Fault Occurrence)

When the current operation side server 3 is operating, the currentoperation side server 3 performs processing of a service requestsupplied from the client unit 9 through the route 73, as shown in FIG.4. Also, the current operation side server 3 transmits the heartbeatsignal (flow B) to the stand-by side server 4 through the route 70.

In this case, each of the communication units 13, 11, 12, and 14receives the heartbeat signal (flow B), outputs the received heartbeatsignal (flow B) to the communication port L, and transmits it to thestand-by side server 4 through the route 70.

Also, the stand-by side server 4 receives the heartbeat signal, and whena reception stop period (a non-reception period) of the heartbeat signaldoes not exceeds the predetermined period, the stand-by side server 4determines that the current operation side server 3 is in the possiblestate of service provision.

(State after Fault Occurrence)

When a fault has occurred in the current operation side server 3, thecurrent operation side server 3 cannot perform the processing of theservice request supplied from the client unit 9 through the route 73.Also, the current operation side server 3 cannot transmit the heartbeatsignal to the stand-by side server 4 through the route 70. Or, thecurrent operation side server 3 in which the fault has occurred stopsthe transmission of the heartbeat signal.

In this case, because the heartbeat signal (flow B) is not received forthe predetermined period, the communication units 13, 11, 12, and 14determine that the flow B has been disconnected. When the flow B isdetermined to have been disconnected, each of the communication units13, 11, 12, and 14 refers to their flow table 111 and performs anoperation based on the “operation information at disconnection”corresponding to the flow B. In an example shown in FIG. 3, each of thecommunication units 13, 11, 12, and 14 controls the flow to be outputtedto the communication port L when receiving the flow of network addressZ. Thus, each of the communication units 13, 11, 12, and 14 transmitsthe service request from the client unit 9 for the stand-by side server4. On the other hand, the communication unit 10 which is not on theroute 70 for the heartbeat signal (flow B) outputs the flow using thenetwork address Z to communication port M as usual. However, the flowwhich is outputted to communication port M from the communication unit10, is changed by the communication unit 11 such that the flow isoutputted onto the route 74. Therefore, the flow using the networkaddress Z and transmitted from the client unit 9 reaches the stand-byside server 4 through the route 74. Therefore, in the present invention,it is necessary to provide the determining section and the switchingsection at least in the communication unit 11 on the route 70 throughwhich the heartbeat signal passes, and the routes 73 and 74 as switchingtargets.

Also, when not receiving the heartbeat signal for the predeterminedperiod, the stand-by side server 4 determines that the current operationside server 3 is in the impossible state of service provision. Whendetermining the impossible state of service provision, the stand-by sideserver 4 shifts to the execution mode, and starts the service performedin the current operation side server 3, by using the network address Zwhich is used by the current operation side server 3. Thus, the stand-byside server 4 takes over the service performed by the current operationside server 3 and the stand-by side server 4 performs processing of theservice request from the client unit 9 by using the route 74, as shownin FIG. 5.

The communication units 13, 11, 12, and 14 in the present exemplaryembodiment change the route into the route 74 between the client unit 9and the stand-by side server 4, when confirming the disconnection of theheartbeat signal (the flow B). As a result, it is possible to earlychange to the network route 74 used when the stand-by side server 4performs the processing in place of the current operation side server 3.

(Operation of Communication System and Effect)

In this way, the communication system of the present exemplaryembodiment is provided with the client unit 9, the current operationside server 3 which performs processing in response to the request fromthe client unit 9, the stand-by side server 4 which performs processingin place of the current operation side server 3 when a fault hasoccurred in the current operation side server 3, and the communicationunits 10 to 14 which build the network routes 73, 74, and 70 between theclient unit 9, the current operation side server 3 and the stand-by sideserver 4. Each of the communication units 10 to 14 is provided with thedetermining section 1121 which determines whether or not the signal(heartbeat signal) which is transmitted from the current operation sideserver 3 to the stand-by side server 4 has been disconnected, and theswitching section 1122 which switches the network route to the route 74used when the client unit 9 and the stand-by side server 4 perform datacommunication when determining when the signal has been disconnected.

Thus, the communication system of the present exemplary embodimentbecomes possible to early perform the switching to the network route 74which is necessary for the stand-by side server 4 to perform theprocessing in place of the current operation side server 3.

Second Exemplary Embodiment

Next, a second exemplary embodiment will be described.

In the first exemplary embodiment, each of the communication units 10 to14 determines whether or not the signal (heartbeat signal) which istransmitted from the current operation side server 3 to the stand-byside server 4 has been disconnected. Then, each of the communicationunits 10 to 14 switches the network route to the route 74 used when theclient unit 9 and the stand-by side server 4 perform data communicationwhen the signal has been disconnected.

In the second exemplary embodiment, as shown in FIG. 6, thecommunication system is provided with a control unit 20 which performsthe integrated control of the communication units 10 to 14. The controlunit 20 determines whether or not the signal (heartbeat signal) which istransmitted from the current operation side server 3 to the stand-byside server 4 has been disconnected. When the signal has beendisconnected, the control unit 20 controls each of the communicationunits 10 to 14 to switch the network route to the route 74 used when theclient unit 9 and the stand-by side server 4 perform data communication.Thus, the control unit 20 can control the communication units 10 to 14and switch the network route to the route 74 used in a case ofperforming data communication by the client unit 9 and the stand-by sideserver 4. Hereinafter, referring to FIG. 6 to FIG. 10, the communicationsystem of the present exemplary embodiment will be described.

<System Configuration of Communication System>

First, referring to FIG. 6, a system configuration of the communicationsystem of the present exemplary embodiment will be described.

The communication system of the present exemplary embodiment is furtherprovided with a control unit 20, compared with the configuration of thecommunication system of the first exemplary embodiment.

The control unit 20 is the unit which communicates with thecommunication units 10 to 14 and which controls the network routesconfigured by the communication units 10 to 14.

The control unit 20 is provided with a communication control section 201and a flow monitoring table 202 as shown in FIG. 7. The communicationcontrol section 201 communicates with the communication units 10 to 14in a peripheral area. The communication control section 201 is providedwith a determining section 2011 and a control section 2012.

The determining section 2011 determines whether or not the network routeshould be switched, based on the heartbeat signal which is transmittedfrom the current operation side server 3 to the stand-by side server 4.The control section 2012 controls the switching operation of the networkroute configured by the communication units 10 to 14 according to thedetermination result by the determining section 2011. The switchingoperation of the network route is performed by transmitting a controlsignal to each of the communication units 10 to 14.

The flow monitoring table 202 manages the “flow information”, the“output port information”, and the “operation information atdisconnection”, like the flow table 111 shown in FIG. 3. With this, thecontrol unit 20 can control a data transfer destination according to theflow information. The information managed by the flow monitoring table202 can be built and changed through a manual operation by using anexternal unit and automatically dynamically by the control unit 20.

The “flow information” is information to specify the identificationinformation of each flow. The “output port information” is informationto specify the communication port which outputs data. The “operationinformation at disconnection” is information showing an operation to bedone when a flow has been disconnected.

When the flow monitoring table 202 is same as that shown in FIG. 3, thecontrol unit 20 operates as follows. That is, when the communicationsystem receives the data in the flow A, the control unit 20 outputs thedata in the flow A from the communication port N, and in a case ofdisconnection (in the state when the flow A has been disconnected), thecontrol unit 20 performs communication control so as to do nothing.Also, when the communication system receives the data in the flow B, thecontrol unit 20 controls to output the data in the flow B from thecommunication port L. On the other hand, in the state that the flow Bhas been disconnected, when one communication unit receives the flow ofa network address Z, the control unit 20 controls each of thecommunication units 10 to 14 to output the flow of the network address Zto the communication port L.

Each of the communication units 10 to 14 is provided with a flow table121 and a communication control section 122, as shown in FIG. 8. Thedifference of the second exemplary embodiment from the first exemplaryembodiment is in that the communication control section 122 in thesecond exemplary embodiment does not have the determining section toswitch the communication route.

The flow table 121 is configured as in the first exemplary embodiment.

The communication control section 122 refers to the flow table 121 andperforms the data transfer processing according to the flow table 121.The communication control section 122 has a switching section 1221.

The switching section 1221 switches the network route in response to acontrol signal received from the control unit 20.

<Processing Operation of Communication System>

Next, referring to FIG. 6, FIG. 9, FIG. 10, the processing operation ofthe communication system of the present exemplary embodiment will bedescribed. FIG. 9 shows the communication route in a state before afault occurs in the current operation side server 3, and FIG. 10 showsthe communication route in a state after the fault has occurred in thecurrent operation side server 3.

(Precondition)

It is supposed that the current operation side server 3 is operatingnormally and that the current operation side server 3 is in the statethat the service request from the client unit 9 can be processed, as theprecondition of the communication system in the present exemplaryembodiment.

When the stand-by side server 4 can receive the heartbeat signalperiodically from the current operation side server 3, the stand-by sideserver 4 determines that the current operation side server 3 is in apossible state of service provision (in an operation state). Thestand-by side server 4 is set to a standby mode when the currentoperation side server 3 is in the possible state of service provision.Also, when the heartbeat signal cannot be received in the predeterminedperiod, the stand-by side server 4 determines that the current operationside server 3 is an impossible state of service provision (in a faultoccurrence state). When the current operation side server 3 is in theimpossible state of service provision, the stand-by side server 4 shiftsto an execution mode. By using the network addresses used by the currentoperation side server 3, the stand-by side server 4 takes over theprocessing being performed by the current operation side server 3.

The communication route between the client unit 9 and the currentoperation side server 3 is the route 73 passing through thecommunication unit 10, the communication unit 11 and the communicationunit 13. The route 73 is defined as using the communication port M. Thecommunication route between the client unit 9 and the stand-by sideserver 4 is the route 74 passing through the communication unit 10, thecommunication unit 11, the communication unit 12 and the communicationunit 14. The route 74 is defined as using the communication port L. Thecommunication route for the heartbeat signal from the current operationside server 3 to the stand-by side server 4 is a route 77 passingthrough the communication unit 13, the control unit 20 and thecommunication unit 14. The route 77 is defined as using thecommunication port L. Also, the flow of the heartbeat signal is definedas the flow B.

It is supposed that the current operation side server 3 and the stand-byside server 4 have mechanisms possible to mutually communicate, in orderto transmit and receive the heartbeat signal. For example, it issupposed that the current operation side server 3 and the stand-by sideserver 4 have the mechanisms which can use a method of assigningaddresses different from an address used for service provision and amethod of using a name solution system and so on.

It is supposed that a network address used to provide a service to theclient unit 9 is defined as Z and that the current operation side server3 is using the network address Z.

(Condition Before Fault Occurrence)

When the current operation side server 3 is operating, the currentoperation side server 3 performs the processing of the service requestsupplied from the client unit 9 through the route 73, as shown in FIG.9. Also, the current operation side server 3 transmits the heartbeatsignal (the flow B) to the stand-by side server 4 through the route 77.

In this case, the communication units 13 and 14 and the control unit 20receives the heartbeat signal (the flow B), and outputs the receivedheartbeat signal (the flow B) to the communication port L and transmitsthe signal to the stand-by side server 4 through the route 77.

Also, the stand-by side server 4 receives the heartbeat signal, and whenthe blind period (the non-reception period) of the heartbeat signal doesnot exceed a predetermined period, the stand-by side server 4 determinesthat the current operation side server 3 is in the possible state ofservice provision.

(Condition after Fault Occurrence)

When a fault has occurred in the current operation side server 3, thecurrent operation side server 3 cannot perform the processing of theservice request supplied from the client unit 9 through the route 73.Also, the current operation side server 3 cannot transmit the heartbeatsignal to the stand-by side server 4 through the route 77. Or, thecurrent operation side server 3 in which the fault has occurred stopsthe transmission of the heartbeat signal.

In this case, because the heartbeat signal (the flow B) is not receivedin the predetermined period, the control unit 20 determines that theflow B has been disconnected. When the flow B is determined to have beendisconnected, the control unit 20 refers to the flow monitoring table202 to switch the operation of the communication units 10 to 14 based onthe “operation information at disconnection” corresponding to the flowB. For example, the control unit 20 outputs a control signal to thecommunication units 10 to 14 according to the flow monitoring table 202shown in FIG. 3. When receiving the flow of network address Z, each ofthe communication units 10 to 14 controls to output the flow to thecommunication port L in response to the control signal. Thus, each ofthe communication units 10 to 14 transmits a service request from theclient unit 9 for the stand-by side server 4. In the present exemplaryembodiment, it is necessary to provide the determining section todetermine the disconnection of the heartbeat signal for the control unit20 on the route 77 which the heartbeat signal passes at least.

Also, when the heartbeat signal cannot be received in the predeterminedperiod, the stand-by side server 4 determines that the current operationside server 3 is the impossible state of service provision. Whendetermining to be in the impossible state of service provision, thestand-by side server 4 shifts to the execution mode and starts theservice having been performed by the current operation side server 3 byusing the network address Z used by the current operation side server 3.Thus, the stand-by side server 4 takes over the service having beenperformed by the current operation side server 3 and performs theprocessing of the service request supplied from the client unit 9through the route 74, as shown in FIG. 10.

When the disconnection of the heartbeat signal (the flow B) isconfirmed, the control unit 20 in the present exemplary embodimentcontrols each of the communication units 10 to 14 to switch the networkroute to the route 74 between the client unit 9 and the stand-by sideserver 4. As a result, the switching of the network route which isnecessary when the stand-by side server 4 performs the processing inplace of the current operation side server 3 (the switching operation tothe route 74) can be early performed. Also, it is possible to reduce theprocessing load of each of the communication units 10 to 14, since it isnot necessary to confirm that the heartbeat signal (the flow B) has beendisconnected.

(Operation of Communication System and Effect)

In this way, the communication system in the present exemplaryembodiment is provided with the client unit 9, the current operationside server 3 which performs processing in response to the request fromthe client unit 9, the stand-by side server 4 which performs theprocessing in place of the current operation side server 3 when a faulthas occurred in the current operation side server 3, the communicationunits 10 to 14 which build network routes 73, 74 and 77 between theclient unit 9, the current operation side server 3 and the stand-by sideserver 4, and the control unit 20 which controls each of thecommunication units 10 to 14. The control unit 20 is provided with thedetermining section 2011 to determine whether or not the signal(heartbeat signal) which is transmitted from the current operation sideserver 3 to the stand-by side server 4 has been disconnected, and thecontrol section 2012 which transmits the control signal to each of thecommunication units 10 to 14 to switch the network route to the route 74used when the client unit 9 and the stand-by side server 4 perform datacommunication, when the determining section 2011 determines that thesignal has been disconnected. Also, each of the communication units 10to 14 is provided with a switching section 1221 to switch the networkroute to the route 74 used when the client unit 9 and the stand-by sideserver 4 perform data communication, when receiving the control signalfrom the control unit 20.

Thus, the communication system of the present exemplary embodiment canearly switch the network route to the route 74 when it is necessary forthe stand-by side server 4 to perform the processing in place of thecurrent operation side server 3. Also, it is possible to reduce theprocessing load of each of the communication units 10 to 14, because itis not necessary to confirm that the heartbeat signal (the flow B) hasbeen disconnected.

It should be noted that in the above exemplary embodiment, the controlunit 20 is provided to determine whether or not the signal (heartbeatsignal) which is transmitted from the current operation side server 3 tothe stand-by side server 4 has been disconnected. However, one of theplurality of communication units 10 to 14 may charge the role of thecontrol unit 20 to perform the above mentioned processing.

Third Exemplary Embodiment

Next, a third exemplary embodiment will be described.

In the first exemplary embodiment, each of the communication units 10 to14 determines whether or not the signal (the heartbeat signal) which istransmitted from the current operation side server 3 to the stand-byside server 4 has been disconnected. Then, each of the communicationunits 10 to 14 switches the network route to the route 74 used when theclient unit 9 and the stand-by side server 4 perform data communication,if the signal has been disconnected.

In the third exemplary embodiment, when the signal is not disconnected(when the transmission of the heartbeat signal is started), each of thecommunication units 10 to 14 switches the network route to the route 73used when the client unit 9 and the current operation side server 3perform data communication. Thus, each of the communication units 10 to14 can early switch the network route to the route 73 when it isnecessary for the current operation side server 3 to perform theprocessing having been performed by the stand-by side server 4.Hereinafter, referring to FIG. 1 to FIG. 2, and FIG. 11 to FIG. 13, thecommunication system of the present exemplary embodiment will bedescribed.

<System Configuration of Communication System>

The communication system of the present exemplary embodiment isconfigured in the same way as the first exemplary embodiment shown inFIG. 1, but the configuration of each of the communication units 11 to14 is different from that of the first exemplary embodiment.

Each of the communication units 11 to 14 in the present exemplaryembodiment has a flow table 111 shown in FIG. 11.

The flow table 111 in the present exemplary embodiment manages the “flowinformation”, the “output port information”, and the “operationinformation at transmission start” as a set, as shown in FIG. 11. Withthis, the communication units 10 to 14 can control a data transferdestination based on the flow information.

The “flow information” is information to specify identificationinformation of each flow. The “output port information” is informationto specify the communication port for data to be outputted. The“operation information at transmission start” is information indicatingan operation to be performed when the flow is started.

For example, the communication units 10 to 14 operate in accordance withthe flow table 111 shown in FIG. 11, as follows. When receiving the dataof the flow A, the communication unit outputs the data of the flow Afrom the communication port N, and performs nothing at the time oftransmission start (when the transmission of the flow A is started).Also, when receiving the data of the flow B, the communication unitoutputs the data of the flow B from the communication port M. On theother hand, when receiving the flow of the network address Z at the timeof transmission start (when the transmission of the flow B is started),the communication unit outputs the flow of the network address Z to thecommunication port M.

<Processing Operation of Communication System>

Next, referring to FIG. 1, FIG. 12, and FIG. 13, the processingoperation of the communication system in the present exemplaryembodiment will be described. FIG. 12 shows the communication route whenthe current operation side server 3 is in the stop state, and FIG. 13shows the communication route when the current operation side server 3is in the operation state.

(Precondition)

It is supposed that the current operation side server 3 is in the stopstate so that the service request from the client unit 9 cannot beprocessed, as the precondition of the communication system in thepresent exemplary embodiment.

When the heartbeat signal cannot be received in the predeterminedperiod, the stand-by side server 4 determines that the current operationside server 3 is the impossible state of service provision (in the faultoccurrence state). When the current operation side server 3 is in theimpossible state of service provision, the stand-by side server 4changes to the execution mode, and by using the network addresses havingbeen used by the current operation side server 3, performs theprocessing in place of the current operation side server 3. Also, whenthe stand-by side server 4 receives the heartbeat signal in thepredetermined period in the standby mode, the stand-by side server 4determines that the current operation side server 3 has returned to thepossible state of service provision (in the operation state). Thestand-by side server 4 changes to the standby mode when the currentoperation side server 3 is in the possible state of service provision.

Referring to FIG. 1, the communication route between the client unit 9and the current operation side server 3 is the route 73 passing throughthe communication unit 10, the communication unit 11 and thecommunication unit 13. The route 73 is defined as using thecommunication port M. The communication route between the client unit 9and the stand-by side server 4 is the route 74 passing through thecommunication unit 10, the communication unit 11, the communication unit12 and the communication unit 14. The route 74 is defined as using thecommunication port L. The communication route of the heartbeat signalfrom the current operation side server 3 to the stand-by side server 4is the route 70 passing through the communication unit 10, thecommunication unit 11, the communication unit 12 and the communicationunit 14. The route 70 is defined as using the communication port L.Also, the flow of the heartbeat signal is defined as the flow B. It issupposed that the current operation side server 3 and the stand-by sideserver 4 have the mechanisms possible to mutually communicate in orderto transmit and receive the heartbeat signal. For example, it issupposed that the current operation side server 3 and the stand-by sideserver 4 have the mechanisms which can use a method of having addressesdifferent from the address used for service provision and a method ofusing a name solution system and so on.

It is supposed that the network addresses used to provide a service tothe client unit 9 are defined as Z and the stand-by side server 4 isusing the network address Z.

(Stopping State)

When the current operation side server 3 is in the stop state, thecurrent operation side server 3 cannot process the service request fromthe client unit 9 by using the route 73. Also, the current operationside server 3 cannot transmit the heartbeat signal to the stand-by sideserver 4 by using the route 70. Or, stopping the current operation sideserver 3 stops the transmission of the heartbeat signal.

In this case, when not receiving the heartbeat signal in thepredetermined period, the stand-by side server 4 determines that thecurrent operation side server 3 is the impossible state of serviceprovision. When determining that the current operation side server 3 isthe impossible state of service provision, the stand-by side server 4changes to the execution mode and performs the processing of the servicerequest from the client unit 9 by using the route 74 and using networkaddress Z, as shown in FIG. 12.

(Operating State)

When the current operation side server 3 is set to the operation state,the current operation side server 3 performs the processing of theservice request from the client unit 9 by using the route 73 as shown inFIG. 13. Also, the current operation side server 3 transmits theheartbeat signal (the flow B) to the stand-by side server 4 through theroute 70.

In this case, when the communication units 13, 11, 12, and 14 receivethe heartbeat signal (the flow B), the communication unit outputs thereceived heartbeat signal (the flow B) to the communication port L andtransmits it to the stand-by side server 4 through the route 70. Also,because receiving the heartbeat signal (the flow B), the communicationunits 13, 11, 12, and 14 determine that the transmission of the flow Bhas been started. When the transmission of the flow B is determined tohave been started, each of the communication units 13, 11, 12, and 14refers to its own flow table 111 and operates based on the transmissionstart operation information corresponding to the flow B. In an exampleshown in FIG. 11, each of the communication units 13, 11, 12, and 14controls to output the flow to the communication port M when receivingthe flow of network address Z. Thus, each of the communication units 13,11, 12, and 14 transmits the service request from the client unit 9 forthe current operation side server 3.

Also, when the stand-by side server 4 receives the heartbeat signal, anda reception stopping period of the heartbeat signal (the non-receptionperiod) does not exceed the predetermined period, the stand-by sideserver 4 determines that the current operation side server 3 is thepossible state of service provision. When determining that the currentoperation side server 3 is in the possible state of service provision,the stand-by side server 4 changes to the standby mode and ends theprocessing.

When it is confirmed that the transmission of the heartbeat signal (theflow B) is started, each of the communication units 13, 11, 12, and 14in the present exemplary embodiment controls to switch the network routeto the route 73 between the client unit 9 and the current operation sideserver 3. As a result, the switching operations to the network route 73is earlier carried out when the current operation side server 3 performsthe processing having been performed by the stand-by side server 4.

(Operation of Communication System and Effect)

In this way, the communication system of the present exemplaryembodiment is provided with the client unit 9, the current operationside server 3 which performs processing in response to a request fromthe client unit 9, the stand-by side server 4 which performs theprocessing in place of the current operation side server 3 when a faulthas occurred in the current operation side server 3, and thecommunication units 10 to 14 which configure network routes 73, 74, and70 between the client unit 9 and the current operation side server 3 orthe stand-by side server 4. Each of the communication units 10 to 14 isprovided with the determining section 1121 to determine whether or notthe signal (the heartbeat signal) which is transmitted from the currentoperation side server 3 to the stand-by side server 4 has beendisconnected, and the switching section 1122 to switch the network routeto the route 73 used when the client unit 9 and the current operationside server 3 perform data communication when the determining section1121 determines that the signal is not disconnected (when thetransmission of the heartbeat signal is started).

With this, the communication system in the present exemplary embodimentcan early switch the network route to the route 73 when the currentoperation side server 3 performs the processing having been performed bythe stand-by side server 4.

It should be noted that the exemplary embodiments mentioned above do notlimit a scope of the present invention, and various modifications arepossible in a range which is not apart from the spirit of the presentinvention.

For example, the above exemplary embodiments can be combined with eachother. Specifically, the mechanism shown in the third exemplaryembodiment which performs a switching operation in case of transmissionstart of the heartbeat signal may be performed in the control unit 20and the communication units 10 to 14 in the second exemplary embodiment.

That is, the control unit 20 is provided with the determining section2011 to determine whether or not the signal (heartbeat signal) which istransmitted from the current operation side server 3 to the stand-byside server 4 has been disconnected, and the control section 2012 whichtransmits the control signal to each of the communication units 10 to 14to switch the network route to the route 73 used when the client unit 9and the current operation side server 3 perform data communication, whenthe determining section 2011 determines that the signal is notdisconnected (when the transmission of the heartbeat signal is started).Also, when receiving the control signal from the control unit 20, eachof the communication units 10 to 14 is provided with the switchingsection 1221 to switch the network route to the route 73 used when theclient unit 9 and the current operation side server 3 perform datacommunication. With this, it becomes possible early switch the networkroute to the route 73 which is necessary for the current operation sideserver 3 to perform the processing having been performed by the stand-byside server 4. Also, each of the communication units 10 to 14 can reducethe processing load because it is not necessary to confirm whether ornot the transmission of the heartbeat signal (the flow B) is started.

Also, a system switching mechanism in disconnection of the heartbeatsignal, as shown in the first and second exemplary embodiments, and asystem switching mechanism in a case of transmission start of theheartbeat signal as shown in the third exemplary embodiment may becombined.

Also, in the above exemplary embodiments, when the heartbeat signal (theflow B) cannot be received in a predetermined period, the flow B isdetermined to have been disconnected. However, if it is possible todetermine whether or not the flow B has been disconnected, any of thetechniques can be applied. For example, if a signal is used in thecommunication protocol to explicitly show communication disconnection,the disconnection of the flow may be recognized based on the signal.

Also, the above exemplary embodiments have been described under thepresupposition of a fail-over. However, the table data managed by theflow table 111 and 121 and the flow monitoring table 202 may bedynamically changed, and the network route may be dynamically switchedusing the changed data. Thus, it is possible to build a configurationwhich is applicable to the cascade fail-over.

Also, the control operation of each of the units of the communicationsystem in the above-mentioned exemplary embodiments may be executed byusing in hardware, software, or in composite manner of both.

It should be noted that when the processing is executed by using thesoftware, it is possible to install a program describing a processingsequence in a memory of a computer which is incorporated into theexclusive-use hardware configuration. Or, the program may be installedin and executed by the general-purpose computer which can executevarious processing.

For example, the program can be recorded in advance in a hard disk andROM (Read Only Memory) as a storage medium. Or, the program can betemporarily or indissolubly stored (recorded) in a removable storagemedium in advance. Such a removable storage medium can be provided asso-called packaged software. It should be noted that as the removablestorage medium, a floppy disk (registered trademark), CD-ROM (CompactDisc-Read Only Memory), MO (Magneto-optical) disk, DVD (DigitalVersatile Disc), a magnetic disk, a semiconductor memory and so on areexemplified.

It should be noted that program installed from the removable storagemedium into the computer. Also, the program may be transferred in radiofrom a download site to the computer. Also, through the network, theprogram may be transferred to the computer by a wire.

Also, the communication system in the present exemplary embodiment, canbe configured not only by executing the processing operation describedin the above exemplary embodiments in a time series but also byexecuting the processing operation in parallel or individually accordingto necessity or according to processing capability of the processor.

The present invention can be applied to Web service, a data center, anda cloud computing system to have a redundancy.

It should be noted that the present patent application claims a priorityon convention based on Japan Patent Application No. 2009-027376 and thedisclosure thereof is incorporated herein by reference.

(Addition 1) ≧Communication System>

The communication system according to the present invention is providedwith a client unit, a first node which performs processing in responseto a request from the client unit, and a second node which performsprocessing in place of the first node when a fault has occurred in thefirst node, and communication units which configure network routes amongthe client unit, the first node and the second node. The communicationunit is provided with a determining section configured to determinewhether or not a signal which is transmitted from the first node to thesecond node has been disconnected, and a switching section configured toswitch the network route between a first network route used when theclient unit and the first node perform data communication, and a secondnetwork route used when the client unit and the second node perform datacommunication. The switching section switches the route based on thedetermination result of the determining section.

(Addition 2)

The communication system according to the present invention is providedwith a client unit, a first node which performs processing in responseto a request from the client unit, a second node which performsprocessing in place of the first node when a fault has occurred in thefirst node, communication units which configure network routes among theclient unit, the first node and the second node, a control unit whichcontrols the communication units. The communication unit is providedwith a switching section which switches the network route between afirst network route used when the client unit and the first node performdata communication, and a second network route used when the client unitand the second node perform data communication. The control unit isprovided with a determining section to determine whether or not a signalwhich is transmitted from the first node to the second node has beendisconnected, and a control section which transmits control signalsbased on the determination result by the determining section to thecommunication units. The switching section switches the network route inresponse to the received control signal from the control unit.

(Addition 3) <Communication Unit>

A communication unit according to the present invention is acommunication unit in a communication system which is provided with aclient unit, a first node which performs processing in response to arequest from the client unit, a second node which performs theprocessing in place of the first node when a fault has occurred in thefirst node, and the communication units which configure the networkroutes among the client unit, the first node and the second node. Thecommunication unit is provided with a determining section to determinewhether or not a signal which is transmitted from the first node to thesecond node has been disconnected, and a switching section whichswitches the network route between a first network route used when theclient unit and the first node perform data communication, and a secondnetwork route used when the client unit and the second node perform datacommunication. The switching section switches the route based on thedetermination result by the determining section.

(Addition 4) <Control Unit>

A control unit according to the present invention is a control unit in acommunication system which is provided with a client unit, a first nodewhich performs processing in response to a request from the client unit,a second node which performs the processing in place of the first nodewhen a fault has occurred in the first node, communication units whichconfigure network routes among the client unit, the first node and thesecond node, and the control unit which controls the communicationunits. The control unit is provided with a determining section todetermine whether or not a signal which is transmitted from the firstnode to the second node has been disconnected, and a control unit whichtransmits control signals to the communication units based on thedetermination result by the determining section, and controls thecommunication units to switch the network rote between the first networkroute used when the client unit and the first node perform datacommunication and the second network route used when the client unit andthe second node perform data communication.

(Addition 5) <Control Method>

A method of controlling according to the present invention is a controlmethod in a communication system which is provided with a client unit, afirst node which performs processing in response to a request from theclient unit, a second node which performs the processing in place of thefirst node when a fault has occurred in the first node, communicationunits which configure network routes among the client unit, the firstnode and the second'node. The control method of present inventionincludes a step of determining whether or not a signal which istransmitted from the first node to the second node has beendisconnected, and a step of switching the network route between a firstnetwork route used when the client unit and the first node perform datacommunication, and a second network route used when the client unit andthe second node perform data communication. The switching includes astep of switching the network route based on the determination result ofthe determining step.

(Addition 6)

A control method according to the present invention is a control methodperformed by a control unit in a communication system which is providedwith a client unit, a first node which performs processing in responseto a request from the client unit, a second node which performs theprocessing in place of the first node when a fault has occurred in thefirst node, communication units which configure network routes among theclient unit, the first node and the second node, and the control unitwhich controls the communication units. The control method of thepresent invention includes a step of determining whether or not a signalwhich is transmitted from the first node to the second node has beendisconnected, and a control step of transmitting control signals to thecommunication units based on the determination result in the determiningstep and controlling the communication units to switch the network routebetween a first network route used when the client unit and the firstnode perform data communication, and a second network route used whenthe client unit and the second node perform data communication.

(Addition 7) <Program>

A program according to the present invention is a program to make acomputer of one of communication units to execute, in a communicationsystem which is provided with a client unit, a first node which performsprocessing in response to a request from the client unit, a second nodewhich performs the processing in place of the first node when a faulthas occurred in the first node, the communication units which configurenetwork routes among the client unit, the first node and the second nodeand the communication system. The program of the present invention makesthe computer to execute a step of determining whether or not a signalwhich is transmitted from the first node to the second node has beendisconnected, and a step of switching the network route between a firstnetwork route used when the client unit and the first node perform datacommunication and a second network route used when the client unit andthe second node perform data communication. Through the switching, thenetwork route can be switched based on the determination result of thedetermining.

(Addition 8)

A program according to the present invention is a program to make acomputer of a control unit to execute, in a communication system whichis provided with a client unit, a first node which performs processingin response to a request from the client unit, a second node whichperforms the processing in place of the first node when a fault hasoccurred in the first node, communication units which configure networkroutes among the client unit, the first node and the second node, andthe control unit which controls the communication units. The program ofthe present invention includes a step of determining whether or not asignal which is transmitted from the first node to the second node hasbeen disconnected, and a control step of transmitting control signals tothe communication units based on the determination result in thedetermining, and controlling the communication units to switch thenetwork route between a first network route used when the client unit,and the first node perform data communication, and a second networkroute used when the client unit and the second node perform datacommunication.

1. A communication system comprising: a client unit; a first nodeconfigured to perform processing in response to a request from saidclient unit; a second node configured to perform the processing in placeof said first node when a fault has occurred in said first node;communication units configured to configure network routes among saidclient unit, said first node and said second node; and a determiningsection provided onto a first network route of said network routes andconfigured to determine whether a signal which is transmitted from saidfirst node to said second node through the first network route has beendisconnected, wherein each of said communication units comprises: aswitching section configured to perform a switching operation between asecond network route of said network routes used when said client unitand said first node perform data communication and a third network routeof said network routes used when said client unit and said second nodeperform data communication, based on the determination result of saiddetermining section.
 2. The communication system according to claim 1,wherein said switching section switches to said third network route fromsaid second network route, when said determining section determines thatsaid signal has been disconnected.
 3. The communication system accordingto claim 1, wherein said switching switches to said second network routefrom said third network route, when said determining section determinesthat said signal is not disconnected.
 4. The communication systemaccording to claim 1, wherein said determining section determines thatthe signal has been disconnected, when a heartbeat signal as the signalwhich is transmitted from said first node to said second node cannot bereceived in a predetermined period, and determines that the signal isnot be disconnected, when said heartbeat signal can be received in thepredetermined period.
 5. The communication system according to claim 1,wherein said determining section and said switching section are bothprovided in each of said communication units which configure said firstand second network routes.
 6. The communication system according toclaim 1, wherein said determining section and said switching section areboth provided in each of said communication units which configure saidfirst, second and third network routes.
 7. The communication systemaccording to claim 1, further comprising a control unit configured tooutput control signals based on the determination result of saiddetermining section, wherein each of said communication units performsthe switching operation in response to one of the control signals.
 8. Acontrol method in a communication system which comprises: a client unit;a first node configured to perform processing in response to a requestfrom said client unit; a second node configured to perform theprocessing in place of said first node when a fault has occurred in saidfirst node; and communication units configured to configure networkroutes among said client unit, said first node and said second node,said control method comprising: determining whether a signal which istransmitted from said first node to said second node through a firstnetwork route of said network routes has been disconnected, onto thefirst network route; and switching a second network route of saidnetwork routes used when said client unit and said first node performdata communication to a third network route of said network routes usedwhen said client unit and said second node perform data communicationbased on the determination result.
 9. The control method according toclaim 8, further comprising: outputting control signals based on saiddetermination result, wherein said switching comprises switching saidsecond network route by said communication units in response to saidcontrol signals.
 10. A computer-readable non-transitory storage mediumwhich stores a computer-executable program code for attaining a controlmethod in a communication system which comprises a client unit, a firstnode configured to perform processing in response to a request from saidclient unit, a second node configured to perform the processing in placeof said first node when a fault has occurred in said first node,communication units which configure network routes among said clientunit, said first node and said second node, and a control unit providedonto a first network route of said network routes, said control methodcomprising: determining that a signal which is transmitted from saidfirst node to said second node through said first network has beendisconnected; and outputting control signals from said control unit tosaid communication units; performing a switching operation between asecond network route of said network routes used when said client unitand said first node perform data communication and a third network routeof said network routes used when said client unit and said second nodeperform data communication, by said communication units in response tosaid control signals.